Magnetic field sensing elements can be used in a variety of applications. In one application, a magnetic field sensing element can be used to detect a direction of a magnetic field, i.e., and angle of the direction of the magnetic field. In another application, a magnetic field sensing element can be used to sense an electrical current. One type of current sensor uses a Hall effect magnetic field sensing element in proximity to a current-carrying conductor.
Planar Hall elements and vertical Hall elements are known types of magnetic field sensing elements. A planar Hall element tends to be responsive to magnetic field perpendicular to a surface of a substrate on which the planar Hall element is formed. A vertical Hall element tends to be responsive to magnetic field parallel to a surface of a substrate on which the vertical Hall element is formed.
Like a vertical Hall element, a conventional magnetoresistance element tends to be responsive to magnetic field parallel to a surface of a substrate on which the magnetoresistance element is formed.
Other types of magnetic field sensing elements are known. For example, a so-called “circular vertical Hall” (CVH) sensing element, which includes a plurality of vertical Hall elements, is known and described in PCT Patent Application No. PCT/EP2008056517, entitled “Magnetic Field Sensor for Measuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008, and published in the English language as PCT Publication No. WO 2008/145662, which application and publication thereof are incorporated by reference herein in their entirety. The CVH sensing element is a circular arrangement of vertical Hall elements arranged over a common circular implant region in a substrate. The CVH sensing element can be used to sense a direction (i.e., an angle) (and optionally a strength) of a magnetic field in a plane of the substrate.
Various parameters characterize the performance of magnetic field sensing elements and magnetic field sensors that use magnetic field sensing elements. These parameters include sensitivity, which is a change in an output signal of a magnetic field sensing element in response to a change of magnetic field experienced by the magnetic sensing element, and linearity, which is a degree to which the output signal of the magnetic field sensing element varies in direct proportion to the magnetic field. These parameters also include an offset, which is characterized by an output signal from the magnetic field sensing element not representative of a zero magnetic field when the magnetic field sensing element experiences a zero magnetic field.
The above-described CVH sensing element is operable, with associated circuits, to provide an output signal representative of an angle of a direction of a magnetic field. Therefore, as described below, if a magnet is disposed upon or otherwise coupled to a so-called “target object,” for example, a camshaft in an engine, the CVH sensing element can be used to provide an output signal representative of an angle of rotation of the target object.
The CVH sensing element is but one element that can provide an output signal representative of an angle of a magnetic field, i.e., an angle sensor. For example, an angle sensor can be provided from a plurality of separate vertical Hall elements or a plurality of magnetoresistance elements.
The magnetic field sensing element, e.g., the CVH sensing element, is limited in a maximum rate at which it can provide signals indicative of the rotational position of the target object. Furthermore, the magnetic field sensing element, e.g., the CVH sensing element, is conventionally operated at one speed, i.e., one sampling rate. Also, generally, power consumption increases at higher sampling rates.
A magnetic field sensor, e.g., a CVH sensing element, is able to achieve a resolution (a number of bits) in a signal representative of the angle of rotation of the target object that decreases with as the rotational speed of the target object increases.
In view of the above, it would be desirable to provide a magnetic field sensor that can adjust certain circuit characteristics within the magnetic field sensor, for example, a sampling rate of the CVH sensing element, as a speed of rotation of the target object increases or decreases, and therefore, the magnetic field sensor can automatically adjust itself to provide characteristics, e.g., resolution, tailored to the speed of rotation of a sensed target object as the target object rotates more rapidly or more slowly.